1. Field of the Invention
An object of the present invention is a device for the protection, against electrostatic discharges, of electronic circuits mounted in modules and inserted into a portable, electrically insulating support such as an electronic card.
A module generally consists of integrated circuits, such as random-access or read-only memories, microprocessors or logic circuits connected to a support by using either a so-called wire technology or a so-called TAB (tape automatic bonding) technology.
The support has, on one of its faces, a network of conducting tracks. The integrated circuit or circuits are mounted on this face. Small conducting wires are respectively soldered to the input/output terminals of the integrated circuit and to the corresponding conducting track of the support.
On the other face of the support, there are contacts. These contacts are accessible from the outside and are each connected to a conducting track. They are used to provide electrical connection between the integrated circuits and the external elements designed to enter into dialogue with them. These contacts are used to transmit to the integrated circuits all the voltages applied thereto by means of the conducting tracks and the wires.
2. Description of the Prior Art
Generally, a drop of thermosetting resin is deposited on the integrated circuits and on their connections with the support in order to protect them. The set forming the integrated circuits and the support constitutes the module which is inserted in an insulating material of the size of an electronic card.
The integrated circuits used in these electronic cards are designed to memorize, protect and, if necessary, make computations on, data coming from outside or data memorized by these cards. They are made with MOS (metal oxide semiconductor) or CMOS (complementary MOS) technology. They are sensitive to electrostatic charges for these charges can damage or even destroy the input and output structures and the supplies by breakdown of oxide or any other irreversible phenomenon.
The electrostatic charges arise on the external contacts under the effect of various frictional forces to which the card may be subjected, or else by contact with a person who is himself or herself charged with a high potential.
Various methods have been used to protect integrated circuits against overvoltages for which they are not designed. In a known method, each external. contact of the module is systematically brought close to a contact carried to the reference potential.
It is known that the breakdown voltage of air is in the range of 100,000 volts per centimeter. The contacts are generally at a distance of a few hundreds of micrometers from each other. When the card or module undergoes an electrostatic discharge, the fact of bringing each contact into close proximity with a contact carried to the reference potential causes an electrical arc between the contact exposed to the discharge and the contact carried to the reference potential. The overvoltage is thus attenuated and is not entirely applied to the integrated circuits.
An object of the present invention is to further reduce the overvoltage applied to the contacts in proposing a device that favors arc effects and reduces the minimum voltage needed to have an arc.